Ferrous alloy



y 16, 1940- A. T. CAPE ET AL 2,208,116

FERROUS ALLOY Original Filed Sept. 6, 1938 %Gr3OL Patented July 16, 1940 UNITED STATES PATENT OFFICE FERROUS ALLOY Arthur T. Cape and Charles V. Foerster, Santa Cruz, Calif.

4 Claims.

This invention relates to ferrous alloys, but has reference more particularly to ferrous alloys which are especially adapted for hard-facing purposes and for utilization in the form of castings.

It is perhaps well-known that there are, in general, three types of hard-facing metals, which,

briefly, are the hard carbides, the non-ferrous type, and the compounds of ferrous materials. In facing a base metal with the hard carbides, the retaining metal flows onto the metal to be faced and becomes welded to it, the carbides not being melted. This type of hard facing alloy is highly resistant to abrasion but it cracks badly and rapidly under repeated impact, and, consequently, its service is limited. Non-ferrous types of hard facing alloys have a relatively good wear resistance, although not as good as the carbides, but are decidedly tougher. The hard-facing alloys of the ferrous type vary greatly and it can be said that the eifectiveness of the material can generally be indicated by the market price thereof. In other words, the cheaper the hard facing metals of the ferrous type are, the lower is their effectiveness. That is, these cheaper materials are too soft and they wear rapidly. On the other hand, the more expensive the hard facing alloy of the ferrous type, the greater tendency they have to be brittle, although they are reasonably resistant to wear.

A primary object of the present invention is to provide ferrous alloys for hard-facing and casting purposes which not only have a high resistance to wear and abrasion, but have high resistance, as well, to heavy and repeated impacts, that is to say, they possess high mechanical strength.

Another object of the invention is to provide ferrous alloys for hard-facing and casting purposes, which are resistant to chemical corrosion,

I to oxidation at high temperatures, and possessing strength at high temperatures.

A further object of the invention is to provide ferrous alloys of the hard-facing type which also possesses the quality of being capable of forming a sound bond with the basemetal.

A still further object of the invention is to provide ferrous alloys of the hard-facing type,

which have a viscosity, in the molten condition, such as to permit exceedingly easy application of the alloys to the base metal.

Other objects of the invention, together with some of the advantageous features thereof, will appear from the following description of the preferred and other embodiments of the invention.

5 It is to be understood, however, that we do not limit ourselves to the embodiments described, since our invention, as defined in the appended claims, can be embodied in a plurality and variety of forms.

The alloys with which we are principally concerned fall into two groups, the alloys in each group having certain properties in common with those of the other group, but having other properties distinct from those of the latter. In order to more clearly visualize these groups, reference may be had to the accompanying drawing, forming a part of the present application, and in which appears a graph containing two curves, all points of which have as their abscissae percentages of nickel, and as their ordinates percentages of chromium.

Referring more particularly to thisgraph, it may be noted that the graphcontains two sets of rectangular coordinates, one set consisting of the axes 0-X(a:-axis) and 0-Y(y-axis), and the other consisting of the axes 0X1(.r1-axis) and 0--Y1(y1-axis) that is, both sets have a common origin (0), but the :ri-axis is inclined at an angle of 60 degrees, measured in a counter-clockwise direction, to the :r-axis. The x-axis denotes percentages of nickel and the -y-axis denotes percentages of chromium.

The graph also contains two curves, designated A and B.

Curve A is a parabola, whose principal axis is the an-axis and whose equation or formula is :mcy1 =a, where a and c are constants, with a=2.7 and c=0.9. To reduce this formula or equation to concentrations of percentages of chromium and nickel, the following is established:

121-0211 must be greater than a, which equals 2.7, where plus .2173 and y minus .4331;

and :1: equals the percentage of nickel and yequals the percentage of chromium. The parabola defined in terms of concentration of chromium and nickel is 2 plus .2173 minus c(% minus A3311) equals a.

The curve Bis generally parabolic, and some what parallel with curve A. No attempt will be made to give the formula or equation of this curve, but it is to be noted that the curve is a dividing line between alloys of different characteristics.

The curve A passes through points or values where there is a critical change of hardness from the austenitic to'the ferritic or more magnetic state. The curve B passes through points or values where the effect of the critical change represented by curve A no longer exists and the hardnesses begin to decrease rapidly. The critical change in hardness from compositions above A to those lying between A and B is accompanied by changes in the magnetic values, from a value of 3 inside the curve to 4 just below curve A, such values being arbitrary but reproducible. The method used for determining these arbitrary values consists in balancing the metal to be tested,

- than the alloys in area No. I, this being due to bringing a magnet to a fixed point and noting the deflection. Such a test readily designates the general physical characteristics of an unknown chromium nickel composition or a known composition to which other alloying elements have been added.

The alloys lying within area No. I are especially adapted for hard-facing, applications, .where softness from the point of view of indentation hardness is of advantage, for resistance to impact. At the same time, the complex chromium carbide plates distributed through the matrix in alloys of this group, plus the fact that the matrix itself is austenitic, and therefore hardens as soon as any work is done, imparts to this group a resistance to wear which-is remarkable. In practice, we have been able to lay down deposits as soft as 30 Rockwell C (approximately 290 Brinell) which are file hard. A preferred, alloy of this group contains about 4.20% carbon, about 14%-18% chromium, about 4%-6% nickel and about .40% vanadium. This alloy is particularly useful in the form of weld rods for hard facing applications for cement mill machinery, agricultural equipment, brick, clay and tile machines, including muller tires; hammer mill parts, and coke handling equipment.

The alloys lying within area No. 2 have a substantially greater initial indentation hardness the tendency of such alloys'to change from the austenitic to the ferritic states. In other words, some of the austenite formed at higher temperatures decomposes duringcooling, and the critical precipitation of carbides gives increased hardness. This occurs in the cast material, and does not require heat treatment to bring it about. Just how critically the hardness values change will appear from the graph, wherein, for example,-an alloy containing 10% chromium and 4% nickel has a hardness of 57 Rockwell C, while an alloy containing 8% chromium and 4% nickel has a hardness of -69 Rockwell C, in the as-cas't state.

The alloys in both groups, that is, in the group within area No. l, and the group within 'area No. 2, preferably contain about 4% carbon, but may contain from about 3% to about 5% carbon.

Vanadium, when added to the aforesaid basic alloys in quantities of from about .20% to about 1%, apparently imparts to the alloys increased toughness, and where the alloys are used in the form of welding rods for hard-facing applica= tions, a degree of stickability, which is definitely advantageous. This term defines the property or'ability of the weld metal, deposited by the melting welding rod, to resist separation from the base metal, under severe impact.

A distinct feature of the invention consists in the addition to the austenitic compositions in area No. l of silicon in amounts suflicient to change these compositions to compositions which are non-magnetic or non-austenitic, with a consequent increase in the hardness of the metal in the as-cast state. For example, the normal hardness of an alloycontaining 4.20% carbon, 16% chromium, 6% nickel and 401% vanadium, in the as-cast state, is 50 Rockwell 0, whereas, when silicon to the extent of 5.5% is added to such alloy, the' hardness increased to 65 Rockwell C. The range of silicon required to effect these changes is from about 1% to about 6%, the upper limit being more or less critical in that additional amounts of silicon result in a substantial decrease in the hardness of .the metal. In general, the more closely the curve A isapproached, the smaller the amount of silicon which is necessary to produce the change in question. In the following table, the arbttrary magnetic values and the hardness for a range of silicon additions is given:

- Msgnet- Hard Sumo ic values ness The silicon-containing material, in the as-welded state, is extremely hard, and has an extremely high wear resistance.

The silicon is preferably added to the alloys in the form of zirconium-silicon or a ferro-alloy containing zirconium and silicon. A particularly desirable alloy in this group, which is magnetic and particularly valuable from the standpoint of wear resistance, contains 4% carbon, 16% chromium, 6% nickel .4% vanadium ing rods, is porous. For arc welding, these factors are not quite as important, because the gases present in the welding rod are removed during the arc weldingprocess. In order-to control the acetylene welding property of the material and also to some extent the arc welding characteristics, a small quantity of alkaline earth or alkali metal is added to the melt. The addition of minutely small quantities of these elements increases the wetting properties of all of the varieties. Without them, during acetylene welding, the metal tends to form into balls, the sur== face is improperly covered and the adherence is not satisfactory. With an immeasurably small amount of sodium, potassium or calcium, the metal melted by the acetylene torch spreads over the surface and covers it excellently. This is a most valuable property, and distinguishes the present alloys from all other welding materials. The addition of calcium to the metal is preferably as calcium silicide. The addition of these elements increases the fluidity of the metal, as well as merely changing the surface tension. The quantity of calcium silicide used is about .07 ounce per pound of metal. The amount used is well in excess of that required.

The arc welding rods are coated with a mixture of plumbago and sodium silicate, to which a small quantity of Bentonite sometimes is added, or they may be coated with a mixture of graphite (in the form of crushed arc furnace electrodes) and sodium silicate, to which Bentonite sometimesis added. The use of these coatings is of considerable interest. Where the rods are coated with plumbago, the deposits are soft; where the rods are coatedwith graphite, the deposits are hard. Differences as great as 30 Rockwell C to Rockwell C can be produced by the selective use of these coatings. The normal mixtures employed in these coatings are as follows, the rods being coated by simply dipping them in the mixture and drying them:

Soft coat Hard coat Grams Plurnbago 3000 ..Sodlu1n silicate 268.0 950 This peculiar effect of plumbago as against graphite is of interest not only in connection with the present alloys, but also in connection with the coating of welding rods formed of other alloys and compositions.

It has been found that where the problem of porosity arises, the addition of fluoride either to the metal itself in the case of castings, or as a thin layer over the graphite coating of the welding rod can be used effectively in eliminating the gas pockets. All of the fluorides are effective in removing gases from the molten metal and in the event of unduly humid conditions causing an absorption of the gases can be eliminated during the freezing process by the addition of the fluoride to the molten metal. In many cases where it is necessary to weld on dirty or gassy cast iron or cast steel the addition of fluoride either with the graphite or plumbago coating, or as a thin layer superimposed upon the the coating, will prevent porosityin the welded deposit.

The alloys should be kept as free from elements other than those described, as possible. In other words, silicon (except where specifically required), manganese, phosphorus and sulphur should be kept to a minimum. For certain specific uses the addition of manganese and phosphorus may have an advantage and these will be described in a later application.

The alloys can be increased in hardness by heating them to 1650 F., and up and cooling them fairly slowly. This is a true precipitation hardening phenomenon.

This application is a division of our co-pending application Serial No. 228,528.

We claim:

1. A ferrous alloy consisting of more than about 3% but not more than about 5% carbon, nickel in amounts .of from about 1% to about 10%, chromium in amounts of from about 8% to about 30%, vanadium in amounts of from about .20% to about 1%, and silicon in amounts of from about 1% to about 6%, the balance of the alloy being iron.

2. A ferrous alloy consisting of more. than 4% but not more than about 5% carbon, nickel in amounts of from about 1% to about 10%, chromium in amounts of from about 8% to about 30% vanadium in amounts of from about 20% to about 1%, and silicon in the amounts of from about 1% to about 6%, the balance of the alloy being iron.

3. A ferrous alloy consisting of about 4% carbon, about 16% chromium, about 6% nickel, about .4% vanadium, and about 4.5% silicon, the balance of the alloy being substantially entirely iron.

4. A ferrous alloy consisting of about 4.20% carbon, about 16% chromium, about 6% nickel, about .40% vanadium, and about 5.5% silicon, the balance of the alloy being substantially entirely iron. 

